Fuel Pump

Fuel injection systems remain under pressure after the engine has been turned OFF. Properly relieve fuel pressure before disconnecting any fuel lines. Failure to do so may result in fire or personal injury.

NOTE

Cover all fuel hose connections with a shop towel, prior to disconnecting, to prevent splash of fuel that could be caused by residual pressure remaining in the fuel line.

Testing

Relieve fuel system pressure.

Disconnect the battery negative cable.

Disconnect the fuel high pressure hose at the delivery pipe side.

CAUTION

Observe all applicable safety precautions when working around fuel. Whenever servicing the fuel system, always work in a well ventilated area. Do not allow fuel spray or vapors to come in contact with a spark or open flame. Keep a dry chemical fire extinguisher near the work area. Always keep fuel in a container specifically designed for fuel storage; also, always properly seal fuel containers to avoid the possibility of fire or explosion.

Connect a fuel pressure gauge to tools MD998709 and MD998742 or exact equivalent, with appropriate adapters, seals and/or gaskets to prevent leaks during the test. Install the gauge and adapter between the delivery pipe and high pressure hose. Install carefully to prevent leaks.

Connect the negative battery cable.

Apply battery voltage to the terminal for fuel pump activation (located in the engine compartment) to run the fuel pump, and check for leaks.

Start the engine and run at curb idle speed.

Measure the fuel pressure and compare to the specifications listed in the chart in Section 1.

Locate and disconnect the vacuum hose running to the fuel pressure regulator. Plug the end of the hose and record the fuel pressure again. The fuel pressure should have increased approximately 10 psi.

Reconnect the vacuum hose the fuel pressure regulator. After the fuel pressure stabilizes, race the engine 2-3 times and check that the fuel pressure does not fall when the engine is running at idle.

Check to be sure there is fuel pressure in the return hose by gently pressing the fuel return hose with fingers while racing the engine. There will be no fuel pressure in the return hose when the volume of fuel flow is low.

If fuel pressure is too low, check for a clogged fuel filter, a defective fuel pressure regulator or a defective fuel pump, any of which will require replacement.

If fuel pressure is too high, the fuel pressure regulator is defective and will have to be replaced or the fuel return is bent or clogged. If the fuel pressure reading does not change when the vacuum hose is disconnected, the hose is clogged or the valve is stuck in the fuel pressure regulator and it will have to be replaced.

Stop the engine and check for changes in the fuel pressure gauge. It should not drop. If the gauge reading does drop, watch the rate of drop. If fuel pressure drops slowly, the likely cause is a leaking injector which will require replacement. If the fuel pressure drops immediately after the engine is stopped, the check valve in the fuel pump isn't closing and the fuel pump will have to be replaced.

Relieve fuel system pressure.

Disconnect the high pressure hose and remove the fuel pressure gauge from the delivery pipe.

Install a new O-ring in the groove of the high pressure hose. Connect the hose to the delivery pipe and tighten the screws. After installation, apply battery voltage to the terminal for fuel pump activation to run the fuel pump. Check for leaks.